Polyamines are essential growth factors for cells. All cells have methods of manufacturing polyamines from amino acid sources. In addition cells can import polyamines from outside the cell via a process referred to as the polyamine transporter (PAT). While much is known about polyamine transport in bacteria, yeast and Leishmania spp., the mammalian polyamine transporter is a measurable, yet poorly described import process. It is an important cancer target because many cancer cells are unable to produce enough polyamines to sustain their growth rate and rely on polyamine import in order to grow. Accordingly, certain polyamines are important vectors for delivery of agents into cells via the cells' polyamine transport system.